1. Field of the Invention
The present invention relates to an XY stage, a head carriage and a tester of magnetic head or magnetic disk. In particular, the present invention relates to a bearing-supported movable stage to be utilized in a low vibration head carriage utilizing a surface plate formed of stone, which can be moved at high speed and rapidly stopped with small stopping position error and can provide a micro positioning suitable for a magnetic head tester or a magnetic disk tester.
2. Prior Art
It is a recent tendency that a composite magnetic head having an MR head, a GMR head and TMR head, etc., which are assembled on a read-out side the head, is used as a magnetic head of a hard disk device. Packaging density of the composite magnetic head is rapidly increased to several GB per inch and the track number thereof is increased to 10,000/inch or more. Further, the track number is still increasing, so that the track width is decreasing. Therefore, a head carriage (a movable base) of a tester for testing a magnetic disk or a magnetic head requires low vibration and highly precise positioning and, moreover, it requires a highly clean environment.
A tester for testing a magnetic disk or a magnetic head, which has a reference base having a surface plate of stone such as gabbro, linear motors mounted on the surface plate and a head carriage (a movable base of the head carriage) supported by air-bearings and tests the magnetic disk or the magnetic head by moving the head carriage, is disclosed in U.S. Pat. No. 6,140,815, of which Application corresponds to JP2002-518777A (referred to as “Reference No. 1”, hereinafter).
On the other hand, with increase of pattern density and/or high miniaturization (or high integration) in the electronic field, an external appearance test on fine defects of a finely processed surface of such as a wiring pattern of a printed circuit board, a semiconductor wafer, a photo mask and a magnetic disk (for example, extraneous material, disconnection of a wiring pattern, short-circuit, protrusion, crack, other defects and pinhole, etc.) is performed by utilizing an air-mount system in which a movable base of an external appearance tester is mounted on a reference base of a stone surface plate. An example of such system is disclosed in JP H5-126973A.
FIG. 6 is a perspective view of a conventional magnetic head tester or a magnetic disk tester disclosed in Reference No. 1.
In FIG. 6, reference numeral 10 depicts a turning stand platform, 12 an air-bearing supported micro positioning carriage, 14 and 18 linear motors, 15 and 19 increment position encoders, 16 an air-bearing spindle carriage and 20 a pedestal formed of granite or gabbro.
The tester disclosed in Reference No. 1 includes an XY stage movable on a stone surface plate. The XY stage has an X axis and a Y axis and is driven along the axes by the respective linear motors 14 and 18 and performs a coarse positioning on one hand and a micro positioning on the other hand, with an aid of piezoelectric actuators. By using the XY stage, the tester tests a magnetic head by positioning the magnetic head in a predetermined track of a magnetic disk supported by the micro positioning carriage.
The feature of the technique disclosed in Reference No. 1 resides in that, in order to move the magnetic head to a predetermined track at high speed and brings it to a sudden stop at the track, the air-bearings are deflated by suction when it is stopped. In more detail, a small recessed region and a large recessed region are formed in the air-bearing supported micro positioning carriage 12 to provide a high vacuum region and a low vacuum region. A stop control of the movable base in the carriage is performed by deflating the regions by suction to lock down the movable base on the stone surface plate to thereby fix it in the predetermined track of the magnetic disk. Further, in the tester disclosed in Reference No. 1, the air-bearing supported micro positioning. carriage 12 and the air-bearing supported spindle carriage 16 can move in one plane by separating the moving axes on the spindle side from the moving axes on the carriage side and thin air film is removed by suction. Therefore, even when a gap between the magnetic disk and the read head becomes minute, a head test can be done with high positional preciseness.
However, since, in the head carriage utilizing the air-bearing supported stone surface plate and using such vacuum lock system, the vacuum suction of air is performed in the stop control of the movable base, it takes a time until the movable base (head carriage) is stopped stably. Further, since the spindle motor system is moved on the reference base of the surface plate, rotational vibration of the spindle is transmitted to the movable positioning system of the spindle in the positioning state and, therefore, there is a problem that the position at which the spindle is positioned may pulsate. This may influence the minute gap between the magnetic disk and the read head, causing a problem that a detection error occurs, S/N ratio is lowered and a high precision head or disk test becomes impossible.